Numerical calculations were conducted to simulate the flow and mass transfer in narrow membrane channels with and without flow disturbers. The channel consists of an impermeable solid wall and a membrane surface with ...Numerical calculations were conducted to simulate the flow and mass transfer in narrow membrane channels with and without flow disturbers. The channel consists of an impermeable solid wall and a membrane surface with a spacing of 2.0 mm. The flow disturbers studied include rectangular winglets, which are often used as longitudinal vortex generators to enhance heat transfer in heat exchanger applications, as well as square prism, triangular prism, and circular cylinder, which are used here to mimic the traditional spacer filaments for comparison of their abilities in enhancing the convective mass transfer near the membrane surface to alleviate the concentration polarization. The disturber performance was evaluated in terms of concentration polarization factor versus consumed pumping power, with a larger factor meaning a more serious concentration polarization.Calculations were carried out for Na Cl solution flow with Reynolds numbers ranging from 400 to 1000. The results show that the traditional flow disturbers can considerably reduce the concentration polarization but cause a substantial pressure drop, while the rectangular winglets can effectively reduce the concentration polarization with a much less pressure drop penalty. The rectangular winglets were optimized in geometry under equal pumping power condition.展开更多
Thermal performance of a heat exchanger duct with punched winglets(PWs)mounted on the upper duct wall has been examined for Reynolds number(Re)ranging from 4100 to 25,500.In the present experiment,two types of PWs:pun...Thermal performance of a heat exchanger duct with punched winglets(PWs)mounted on the upper duct wall has been examined for Reynolds number(Re)ranging from 4100 to 25,500.In the present experiment,two types of PWs:punched delta-and elliptical-winglets(P-DW and P-EW)with four punched-hole sizes were tested at a fixed attack angle,optimal relative pitch and height.Also,data of solid delta-and elliptical-winglets(DW and EW)were included for comparison.The investigation has shown that the P-DW yields higher thermal-performance enhancement factor(η)than the P-EW.Although the solid DW and EW with no punch have the highest heat transfer and friction loss,the PWs yield betterηthan the solid ones.For PWs,the P-DW with smaller hole size has the peak heat transfer and friction loss around 5.7 and 40 times over the smooth duct,respectively but the optimumηof 2.17 is seen for the one with a certain hole size.The PWs provideηat about 5%–8%above the solid winglets.展开更多
Taking a two-stage variable-pitch axial fan as the research object,five schemes,including a single counter-flow rib layout grooved tip,are numerically simulated using the fluent software.The results indicate that,comp...Taking a two-stage variable-pitch axial fan as the research object,five schemes,including a single counter-flow rib layout grooved tip,are numerically simulated using the fluent software.The results indicate that,compared with the original blade tip,the total pressure rise and efficiency of the four proposed schemes have been improved to various degrees,with Scheme 4(groove tip with double counterflow ribs)displaying the best performances.The total pressure and efficiency are increased by 113.44 Pa and 0.955%,respectively.The blade tip leakage flow is reduced to varying degrees under different schemes,according to the following order:Scheme 1,Scheme 2,Scheme 4,and Scheme 3 leading to a reduction of 7.44%,6.46%,5.36%,and 4.35%,respectively.Steady results are used as the initial condition for the ensuing strength check and modal analysis.展开更多
In this paper we discussed the development of a morphing wingtip device or winglet for aircraft.The aim of this research is enhancing the aerodynamic of aircrafts,by optimizing the winglet shape,angle and torsion,to r...In this paper we discussed the development of a morphing wingtip device or winglet for aircraft.The aim of this research is enhancing the aerodynamic of aircrafts,by optimizing the winglet shape,angle and torsion,to reduce wingtip vortices at each flight stage,reduce drag,fuel consumption and increase its endurance.The development of a working physical wingtip device with morphing functionality,is possible by using piezoelectric MFCs(Macro Fiber Composites)as actuators in wing structures.Due to their excellent properties like flexibility,light weight,tolerant to damage and long term stability MFC fit most of the requirements and specifications of morphing structures.Unfortunately,they are based on the toxic compound of PbZrxTi1-xO3(PZT).Lead-free materials can replace lead based compounds.Also,other aim of this inquiry is the development of piezoelectric lead-free compounds based on the solid solution Ba1-xCaxTi0.9Zr0.1O3(BCZT)with x=0.1,0.125,0.15.The reason for choosing these compositions is because BZCT compounds could reach a piezoelectricity coefficient d33~400 pC/N.This value is comparable with commercial PZT,therefore it is a great candidate to replace it.展开更多
随着空中交通流量的增长,尾流间隔精细化、动态化缩减成为民航发展的一种趋势,研究尾流演化过程也成为民航领域关注的前沿科学问题。基于此,采用雷诺平均N-S方程方法研究了B737-800飞机有无融合式翼梢小翼对飞机尾涡的演化过程影响。利...随着空中交通流量的增长,尾流间隔精细化、动态化缩减成为民航发展的一种趋势,研究尾流演化过程也成为民航领域关注的前沿科学问题。基于此,采用雷诺平均N-S方程方法研究了B737-800飞机有无融合式翼梢小翼对飞机尾涡的演化过程影响。利用美国国家航空航天局(National Aeronautics and Space Administration,NASA)动态尾流系统中尾涡消散模型(aircraft vortex spacing system prediction algorithm,APA)计算了不同气象环境参数下有无小翼的尾涡环量变化。结果表明:融合式翼梢小翼可以分割翼尖涡,有效改变翼尖气流的流动特性,增大速度梯度,减小尾涡速度、尾涡能量集中程度和尾涡强度;不同大气湍流耗散率和大气层结稳定度下,小翼对尾涡强度的减小量不同。展开更多
基金Supported by Tsinghua University Initiative Scientific Research Program(20131089319)
文摘Numerical calculations were conducted to simulate the flow and mass transfer in narrow membrane channels with and without flow disturbers. The channel consists of an impermeable solid wall and a membrane surface with a spacing of 2.0 mm. The flow disturbers studied include rectangular winglets, which are often used as longitudinal vortex generators to enhance heat transfer in heat exchanger applications, as well as square prism, triangular prism, and circular cylinder, which are used here to mimic the traditional spacer filaments for comparison of their abilities in enhancing the convective mass transfer near the membrane surface to alleviate the concentration polarization. The disturber performance was evaluated in terms of concentration polarization factor versus consumed pumping power, with a larger factor meaning a more serious concentration polarization.Calculations were carried out for Na Cl solution flow with Reynolds numbers ranging from 400 to 1000. The results show that the traditional flow disturbers can considerably reduce the concentration polarization but cause a substantial pressure drop, while the rectangular winglets can effectively reduce the concentration polarization with a much less pressure drop penalty. The rectangular winglets were optimized in geometry under equal pumping power condition.
文摘Thermal performance of a heat exchanger duct with punched winglets(PWs)mounted on the upper duct wall has been examined for Reynolds number(Re)ranging from 4100 to 25,500.In the present experiment,two types of PWs:punched delta-and elliptical-winglets(P-DW and P-EW)with four punched-hole sizes were tested at a fixed attack angle,optimal relative pitch and height.Also,data of solid delta-and elliptical-winglets(DW and EW)were included for comparison.The investigation has shown that the P-DW yields higher thermal-performance enhancement factor(η)than the P-EW.Although the solid DW and EW with no punch have the highest heat transfer and friction loss,the PWs yield betterηthan the solid ones.For PWs,the P-DW with smaller hole size has the peak heat transfer and friction loss around 5.7 and 40 times over the smooth duct,respectively but the optimumηof 2.17 is seen for the one with a certain hole size.The PWs provideηat about 5%–8%above the solid winglets.
基金This research is supported by the Fundamental Research Funds for the Central Universities(No.2021 MS121).
文摘Taking a two-stage variable-pitch axial fan as the research object,five schemes,including a single counter-flow rib layout grooved tip,are numerically simulated using the fluent software.The results indicate that,compared with the original blade tip,the total pressure rise and efficiency of the four proposed schemes have been improved to various degrees,with Scheme 4(groove tip with double counterflow ribs)displaying the best performances.The total pressure and efficiency are increased by 113.44 Pa and 0.955%,respectively.The blade tip leakage flow is reduced to varying degrees under different schemes,according to the following order:Scheme 1,Scheme 2,Scheme 4,and Scheme 3 leading to a reduction of 7.44%,6.46%,5.36%,and 4.35%,respectively.Steady results are used as the initial condition for the ensuing strength check and modal analysis.
文摘In this paper we discussed the development of a morphing wingtip device or winglet for aircraft.The aim of this research is enhancing the aerodynamic of aircrafts,by optimizing the winglet shape,angle and torsion,to reduce wingtip vortices at each flight stage,reduce drag,fuel consumption and increase its endurance.The development of a working physical wingtip device with morphing functionality,is possible by using piezoelectric MFCs(Macro Fiber Composites)as actuators in wing structures.Due to their excellent properties like flexibility,light weight,tolerant to damage and long term stability MFC fit most of the requirements and specifications of morphing structures.Unfortunately,they are based on the toxic compound of PbZrxTi1-xO3(PZT).Lead-free materials can replace lead based compounds.Also,other aim of this inquiry is the development of piezoelectric lead-free compounds based on the solid solution Ba1-xCaxTi0.9Zr0.1O3(BCZT)with x=0.1,0.125,0.15.The reason for choosing these compositions is because BZCT compounds could reach a piezoelectricity coefficient d33~400 pC/N.This value is comparable with commercial PZT,therefore it is a great candidate to replace it.
文摘随着空中交通流量的增长,尾流间隔精细化、动态化缩减成为民航发展的一种趋势,研究尾流演化过程也成为民航领域关注的前沿科学问题。基于此,采用雷诺平均N-S方程方法研究了B737-800飞机有无融合式翼梢小翼对飞机尾涡的演化过程影响。利用美国国家航空航天局(National Aeronautics and Space Administration,NASA)动态尾流系统中尾涡消散模型(aircraft vortex spacing system prediction algorithm,APA)计算了不同气象环境参数下有无小翼的尾涡环量变化。结果表明:融合式翼梢小翼可以分割翼尖涡,有效改变翼尖气流的流动特性,增大速度梯度,减小尾涡速度、尾涡能量集中程度和尾涡强度;不同大气湍流耗散率和大气层结稳定度下,小翼对尾涡强度的减小量不同。
